Backside-Illuminated Photodetector Structure and Method of Making the Same

ABSTRACT

A backside-illuminated photodetector structure includes a first reflecting region, a second reflecting region and a semiconductor region. The semiconductor region is between the first reflecting region and the second reflecting region. The semiconductor region comprises a first doped region and a second doped region.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/876,666, entitled “Backside-Illuminated Photodetector Structure andMethod of Making the Same,” filed on Jan. 22, 2018, which is acontinuation of U.S. patent application Ser. No. 14/087,011, entitled“Backside-Illuminated Photodetector Structure and Method of Making theSame,” filed on Nov. 22, 2013, now U.S. Pat. No. 9,876,127 issued Jan.23, 2018, which applications are incorporated herein by reference.

BACKGROUND

In semiconductor technologies, image sensors are used for sensing avolume of exposed light projected towards the semiconductor substrate.Backside-illuminated photodetectors are an example of an image sensorfor sensing a volume of radiation (e.g., light) projected towards theback surface of a semiconductor substrate. The photodetectors may beformed on the front side of the substrate, the substrate being thinenough to allow the radiation incident on the back surface of thesubstrate to reach the photodetectors.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments are illustrated by way of example, and not bylimitation, in the figures of the accompanying drawings, whereinelements having the same reference numeral designations represent likeelements throughout. It is emphasized that, in accordance with standardpractice in the industry various features may not be drawn to scale andare used for illustration purposes only. In fact, the dimensions of thevarious features in the drawings may be arbitrarily increased or reducedfor clarity of discussion.

FIG. 1 is a cross sectional view of a Backside-Illuminated (BSI)Photodetector structure in accordance with one or more embodiments;

FIG. 2 is a cross sectional view of a BSI Photodetector structure inaccordance with one or more embodiments; and

FIG. 3 is a flow chart of a method of making a BSI Photodetectorstructure in accordance with one or more embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosed subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are examples and are notintended to be limiting.

This description of the embodiments is intended to be read in connectionwith the accompanying drawings, which are to be considered part of theentire written description. In the description, relative terms such as“before,” “after,” “above,” “below,” “up,” “down,” “top” and “bottom” aswell as derivative thereof (e.g., “horizontally,” “downwardly,”“upwardly,” etc.) should be construed to refer to the orientation asthen described or as shown in the drawing under discussion. Theserelative terms are for convenience of description and do not requirethat the system be constructed or operated in a particular orientation.Terms concerning attachments, coupling and the like, such as “connected”and “interconnected,” refer to a relationship wherein components areattached to one another either directly or indirectly throughintervening components, unless expressly described otherwise.

FIG. 1 is a cross-sectional view of a BSI photodetector structure 100 inaccordance with one or more embodiments. BSI photodetector structure 100comprises a semiconductor region 102 between a first reflecting region104 and a second reflecting region 106. First reflecting region 104 isover the semiconductor region 102. Semiconductor region 102 is oversecond reflecting region 106. In some embodiments, the first reflectingregion 104 or the second reflecting region 106 is flush against thesemiconductor region 102.

First reflecting region 104 is over semiconductor region 102. Firstreflecting region 104 includes layers of materials, e.g., firstreflecting layers 104 a, 104 b and 104 c, having correspondingrefractive indices, e.g., n₁₀₄ _(a) , n₁₀₄ _(b) and n₁₀₄ _(c) , toreflect incident electromagnetic radiation, and improving the efficiencyof the BSI photodetector structure 100. In some embodiments, firstreflecting region 104 is a distributed Bragg reflector, which usesalternating layers of materials having different refractive indices toreflect emitted light from semiconductor region 102. In someembodiments, the first reflecting region 104 is flush againstsemiconductor region 102.

First reflecting region 104 includes first reflecting layers 104 a, 104b and 104 c. In some embodiments, first reflecting region 104 includesone or more reflecting layers. First reflecting layer 104 c is overfirst reflecting layer 104 b and first reflecting layer 104 a. Firstreflecting layer 104 b is over first reflecting layer 104 a. Firstreflecting layer 104 a is over semiconductor region 102.

In some embodiments, first reflecting region 104 is in a two-dimensionalplane which is parallel to the semiconductor region 102. In someembodiments, first reflecting region 104 is a three-dimensionalstructure over semiconductor region 102. In some embodiments, each firstreflecting layer 104 a, 104 b and 104 c is in a two-dimensional planewhich is parallel to each first reflecting layer 104 a, 104 b and 104 c.

In some embodiments, first reflecting region 104 comprises a stack ofalternating layers of reflecting materials, e.g., first reflectinglayers 104 a, 104 b and 104 c, with alternating high and low refractiveindices. In some embodiments, first reflecting layers 104 a and 104 care the same material and the corresponding indices of refraction, n₁₀₄_(a) and n₁₀₄ _(c) , are equal. In some embodiments, first reflectinglayer 104 a is a different material from first reflecting layer 104 b,and the corresponding indices of refraction, n₁₀₄ _(a) and n₁₀₄ _(b) ,are not equal. In some embodiments, first reflecting layer 104 c is adifferent material from first reflecting layer 104 b, and thecorresponding indices of refraction, n₁₀₄ _(c) and n₁₀₄ _(b) , are notequal.

In some embodiments, the refraction index contrast of each alternatinghigh and low refractive index is about 0.5 or greater. In someembodiments, one or more of first reflecting layers 104 a, 104 b and 104c include high refractive index materials comprising SiNx, AlN, Si,high-k dielectrics; any other suitable material; or combinationsthereof. In some embodiments, one or more of first reflecting layers 104a, 104 b and 104 c include low refractive index materials comprisingSiO₂, low-k dielectrics; any other suitable material; or combinationsthereof. In some embodiments, at a wavelength ranging from about 1.0 μmto about 3.0 μm, the index of refraction (n₁₀₄ _(b) ) for the firstreflecting layer 104 b ranges from about 1.3 to about 2.0. In someembodiments, at a wavelength ranging from about 1.0 μm to about 3.0 μm,the index of refraction (n₁₀₄ _(a) ) for the first reflecting layer 104a ranges from about 1.6 to about 2.8. In some embodiments, at awavelength ranging from about 1.0 μm to about 3.0 μm, the index ofrefraction (n₁₀₄ _(c) ) for the first reflecting layer 104 c ranges fromabout 1.6 to about 2.8.

In some embodiments, a reflectivity of the first reflecting region 104ranges from about 20% to about 80%. In some embodiments, the firstreflecting region 104 allows incident radiation to be transmittedthrough the first reflecting region 104 functioning as an opticalwindow. In some embodiments, the number of first reflecting layersranges from about 2 layers to about 20 layers. In some embodiments, thethickness of each first reflecting layer 104 a, 104 b and 104 c rangesfrom about 60 nm to about 500 nm. In some embodiments, the firstreflecting region 104 is formed by CVD, ALD, or other processes. In someembodiments, the first reflecting region 104 has a multilayer structureand is formed in a multiple-step process. In some embodiments, thethickness of each first reflecting layer 104 a, 104 b and 104 c iscontrolled in order to collect sufficient radiation. In someembodiments, the semiconductor region 102 is grinded to a thicknessrange of about 0.5 μm to about 5 μm. In some embodiments, the thicknessof each first reflecting layer 104 a, 104 b and 104 c is controlled bychemical mechanical polishing (CMP) or wet etch smoothing of the firstside 102 a of semiconductor region 102 after grinding/polishing. In someembodiments, the smoothing of the first side 102 a of semiconductorregion includes silicon wet etching for top surface roughness control.In some embodiments, the silicon wet etching includes using TMAH or KOH;any other suitable material; or combinations thereof; and a maskincluding SiNx, SiO₂ or Cu; any other suitable material; or combinationsthereof.

Semiconductor region 102 is over second reflecting region 106.Semiconductor region 102 includes a first side 102 a, a second side 102b, a central semiconductor region 102 c, a first doped region 108 and asecond doped region 110. The second side 102 b of semiconductor region102 is an opposite side of the semiconductor region 102 from the firstside 102 a. The central semiconductor region 102 c is between a firstdoped region 108 of the semiconductor region and a second doped region110. In some embodiments, the second side 102 b is along thesemiconductor region 102/second reflecting region 106 interface. In someembodiments, the first side 102 a is along the semiconductor region102/first reflecting region 104 interface. In some embodiments, thesecond side 102 b is adjacent to the second reflecting region 106. Insome embodiments, the first side 102 a is adjacent to the firstreflecting region 104. In some embodiments, the second side 102 b is afrontside surface of the BSI photodetector 100. In some embodiments, thefirst side 102 a is a backside surface of the BSI photodetector 100.

In some embodiments, semiconductor region 102 is in a two-dimensionalplane which is parallel to the second reflecting region 106. In someembodiments, semiconductor region 102 is a three-dimensional structureover second reflecting region 106. In some embodiments, first dopedregion 108 is positioned in an upper portion of semiconductor region102. In some embodiments, first doped region 108 is adjacent to thefirst side 102 a of semiconductor region 102. In some embodiments,second doped region 110 is positioned in a lower portion ofsemiconductor region 102. In some embodiments, second doped region 110is adjacent to the second reflecting region 106. In some embodiments,second doped region 110 is adjacent to the second side 102 b ofsemiconductor region 102.

In some embodiments, semiconductor region 102 is a P-I-N junction, wherethe P-region and N-region include first doped region 108 and the seconddoped region 110, and the I-region includes a lightly dopednear-intrinsic semiconductor region 102. In some embodiments, thesemiconductor region 102 includes a bulk material or a quantum well. Insome embodiments, the quantum well includes a single quantum well. Insome embodiments, the quantum well includes multiple quantum wellsincluding multiple layers. In some embodiments, the number of quantumwell layers ranges from about 1 layer to about 10 layers. In someembodiments, the quantum well includes a layer of Si, Ge, SiGe, SiC,GeSn, SiGeSn or GaN. In some embodiments, the multiple quantum wellincludes alternating layers of Si, Ge, SiGe, SiC, GeSn, SiGeSn or GaN.In some embodiments, the bulk material includes an elementalsemiconductor including silicon or germanium in crystal,polycrystalline, or an amorphous structure, an alloy semiconductorincluding SiGe, SiC, GeSn, SiGeSn or GaN; any other suitable material;or combinations thereof. In some embodiments, the thickness of thesemiconductor region 102 ranges from about 0.2 μm to about 5 μm. In someembodiments, the semiconductor region 102 is formed in amultiple-stepprocess.

First doped region 108 is over the second doped region 110 and thesecond reflecting region 106. First doped region 108 includes a firsttransverse region 108 a, a first contact region 108 b and a secondcontact region 108 c. In some embodiments, first transverse region 108 ais across the semiconductor region 102 in a substantially horizontaldirection, e.g., x-direction. In some embodiments, first transverseregion 108 a, first contact region 108 b or second contact region 108 cis positioned in an upper portion of semiconductor region 102.

In some embodiments, first doped region 108 is in a two-dimensionalplane which is parallel to the second reflecting region 106. In someembodiments, first doped region 108 is a three-dimensional structureover the second doped region 110 and the second reflecting region 106.In some embodiments, first doped region 108 is along the semiconductorregion 102/first reflecting region 104 interface.

In some embodiments, first transverse region 108 a is in atwo-dimensional plane which is parallel to the second reflecting region106. In some embodiments, first transverse region 108 a is athree-dimensional structure over second doped region 110 and the secondreflecting region 106. In some embodiments, first transverse region 108a is parallel to the semiconductor region 102/first reflecting region104 interface. In some embodiments, first transverse region 108 a isacross the semiconductor region 102.

In some embodiments, first contact region 108 b is in a two-dimensionalplane which is parallel to the second reflecting region 106. In someembodiments, first contact region 108 b is a three-dimensional structureover second doped region 110 and the second reflecting region 106. Insome embodiments, second contact region 108 c is in a two-dimensionalplane which is parallel to the second reflecting region 106. In someembodiments, second contact region 108 c is a three-dimensionalstructure over second doped region 110 and the second reflecting region106. In some embodiments, first contact region 108 b is electricallyconnected to first conductive line 116. In some embodiments, secondcontact region 108 c is electrically connected to second conductive line118.

In some embodiments, second contact region 108 c is in a two-dimensionalplane which is parallel to the first contact region 108 b. In someembodiments, first contact region 108 b and second contact region 108 chave substantially equal vertical positioning with respect to the firstreflecting region 104. In some embodiments, first contact region 108 band second contact region 108 c have different vertical positioning withrespect to the first reflecting region 104. In some embodiments, firstcontact region 108 b and second contact region 108 c are the same heightwith respect to the first reflecting region 104. In some embodiments,first contact region 108 b and second contact region 108 c are adifferent height with respect to the first reflecting region 104. Insome embodiments, first transverse region 108 a, first contact region108 b or second contact region 108 c has a multilayer structure.

Second doped region 110 is over the second reflecting region 106. Insome embodiments, second doped region 110 is in a two-dimensional planewhich is parallel to the second reflecting region 106. In someembodiments, second doped region 110 is a three-dimensional structureover second reflecting region 106. In some embodiments, second dopedregion 110 is along the semiconductor region 102/second reflectingregion 106 interface. In some embodiments, second doped region 110 is ina lower portion of semiconductor region 102. In some embodiments, seconddoped region 110 is a contact electrically connected to the thirdconductive line 120.

In some embodiments, first doped region 108 or second doped region 110are doped with dopants utilized for Si, Ge, SiGe, SiC, GeSn, SiGeSn orGaN. In some embodiments, first doped region 108 is doped with an n-typematerial, including Phosphorous, Arsenic or Antimony, or any othersuitable material, and second doped region 110 is doped with a p-typematerial, including Boron, or any other suitable material. In someembodiments, first doped region 108 is doped with a p-type material,including Boron, or any other suitable material, and second doped region110 is doped with an n-type material, including Phosphorous, Arsenic orAntimony, or any other suitable material.

In some embodiments, the thickness of the first transverse region 108 aranges from about 20 nm to about 500 nm. In some embodiments, thethickness of the first contact region 108 b ranges from about 10 nm toabout 100 nm. In some embodiments, the thickness of the second contactregion 108 c ranges from about 10 nm to about 100 nm. In someembodiments, the thickness of the second doped region 110 ranges fromabout 20 nm to about 200 nm.

In some embodiments, the dopant concentration of the first transverseregion 108 a ranges from about equal to or greater than 10¹⁸ ions/cm³.In some embodiments, the dopant concentration of the first contactregion 108 b ranges from about equal to or greater than 10¹⁹ ions/cm³.In some embodiments, the dopant concentration of the second contactregion 108 b ranges from about equal to or greater than 10¹⁹ ions/cm³.In some embodiments, the dopant concentration of the second doped region110 ranges from about equal to or greater than 10¹⁸ ions/cm³. In someembodiments, the dopant concentration of the first transverse region 108a is equal to the dopant concentration of the first contact region 108 bor the second contact region 108 b. In some embodiments, the dopantconcentration of the first transverse region 108 a is different from thedopant concentration of the first contact region 108 b or the secondcontact region 108 b. In some embodiments, the dopant concentration ofthe first contact region 108 b is equal to the dopant concentration ofthe second contact region 108 b. In some embodiments, the dopantconcentration of the first contact region 108 b is different from thedopant concentration of the second contact region 108 b.

First insulating region 112 extends circumferentially around the outersurface of first conductive line 116. First insulating region 112electrically isolates the first conductive line 116 from the seconddoped region 110. First insulating region 112 electrically isolates thefirst doped region 108 from the second doped region 110. In someembodiments, the first insulating region 112 includes a dielectricmaterial including SiO₂, SiNx or low-k dielectric; any other suitablematerial; or combinations thereof. A low-k dielectric material has adielectric constant less than that of silicon dioxide. In someembodiments, the first insulating region 112 is formed by chemical vapordeposition (CVD), atomic layer deposition (ALD), or other processes. Insome embodiments, a thickness of the first insulating region 112 rangesfrom about 100 nm to about 3000 nm.

Second insulating region 114 extends circumferentially around the outersurface of second conductive line 118. Second insulating region 114electrically isolates the second conductive line 118 from the seconddoped region 110. Second insulating region 114 electrically isolates thefirst doped region 108 from the second doped region 110. In someembodiments, the second insulating region 114 includes a dielectricmaterial including SiO₂, SiNx or low-k dielectric; any other suitablematerial; or combinations thereof. In some embodiments, the secondinsulating region 114 is formed by chemical vapor deposition (CVD),atomic layer deposition (ALD), or other processes. In some embodiments,a thickness of the second insulating region 114 ranges from about 100 nmto about 3000 nm.

Second reflecting region 106 is below semiconductor region 102. Secondreflecting region 106 includes layers of materials, e.g., secondreflecting layers 106 a, 106 b, 106 c, 106 d and 106 e, havingcorresponding refractive indices, e.g., n_(106a), n_(106b), n_(106c),n_(106d), and n_(106e). Second reflecting region 106 reflects incidentelectromagnetic radiation, and improves the efficiency of the BSIphotodetector structure 100. In some embodiments, second reflectingregion 106 is a distributed Bragg reflector, which uses alternatinglayers of materials having different refractive indices to reflectemitted light from semiconductor region 102. In some embodiments, thesecond reflecting region 106 is flush against semiconductor region 102.

Second reflecting region 106 includes second reflecting layers 106 a,106 b, 106 c, 106 d and 106 e. In some embodiments, second reflectingregion 106 includes one or more reflecting layers. Second reflectinglayer 106 e is over second reflecting layer 106 d, second reflectinglayer 106 c, second reflecting layer 106 b and second reflecting layer106 a. Second reflecting layer 106 d is over second reflecting layer 106c, second reflecting layer 106 b and second reflecting layer 106 a.Second reflecting layer 106 c is over second reflecting layer 106 b andsecond reflecting layer 106 a. Second reflecting layer 106 b is oversecond reflecting layer 106 a.

In some embodiments, second reflecting region 106 is in atwo-dimensional plane which is parallel to the semiconductor region 102.In some embodiments, second reflecting region 106 is a three-dimensionalstructure over first conductive layer 122, second conductive layer 124and third conductive layer 126. In some embodiments, each secondreflecting layer 106 a, 106 b, 106 c, 106 d and 106 e is in atwo-dimensional plane which is parallel to each second reflecting layer106 a, 106 b, 106 c, 106 d and 106 e.

In some embodiments, second reflecting region 106 comprises a stack ofalternating layers of reflecting materials, e.g., second reflectinglayers 106 a, 106 b, 106 c, 106 d and 106 e, with alternating high andlow refractive indices. In some embodiments, second reflecting layers106 a and 106 c are the same material and the corresponding indices ofrefraction, n₁₀₆ _(a) and n₁₀₆ _(c) , are equal. In some embodiments,second reflecting layers 106 c and 106 e are the same material and thecorresponding indices of refraction, n₁₀₆ _(c) and n₁₀₆ _(e) , areequal. In some embodiments, second reflecting layers 106 a and 106 e arethe same material and the corresponding indices of refraction, n₁₀₆ _(a)and n₁₀₆ _(e) , are equal. In some embodiments, second reflecting layers106 b and 106 d are the same material and the corresponding indices ofrefraction, n₁₀₆ _(b) and n₁₀₆ _(a) , are equal. In some embodiments,second reflecting layer 106 a is a different material from secondreflecting layer 106 b, and the corresponding indices of refraction,n₁₀₆ _(a) and n₁₀₆ _(b) , are not equal. In some embodiments, secondreflecting layer 106 c is a different material from second reflectinglayer 106 b, and the corresponding indices of refraction, n₁₀₆ _(c) andn₁₀₆ _(b) , are not equal. In some embodiments, second reflecting layer106 c is a different material from second reflecting layer 106 d, andthe corresponding indices of refraction, n₁₀₆ _(c) and n₁₀₆ _(a) , arenot equal. In some embodiments, second reflecting layer 106 e is adifferent material from second reflecting layer 106 d, and thecorresponding indices of refraction, n₁₀₆ _(e) and n₁₀₆ _(a) , are notequal.

In some embodiments, the refraction index contrast of each alternatinghigh and low refractive index is about 0.5 or greater. In someembodiments, one or more of second reflecting layers 106 a, 106 b, 106c, 106 d or 106 e include high refractive index materials comprisingSiNx, AlN, Si, high-k dielectrics; any other suitable material; orcombinations thereof. In some embodiments, one or more of secondreflecting layers 106 a, 106 b, 106 c, 106 d or 106 e include lowrefractive index materials comprising SiO₂, low-k dielectrics; any othersuitable material; or combinations thereof. In some embodiments, at awavelength ranging from about 1.0 μm to about 3.0 μm, the index ofrefraction (n₁₀₆ _(a) ) for the second reflecting layer 106 a rangesfrom about 1.3 to about 2.0. In some embodiments, at a wavelengthranging from about 1.0 μm to about 3.0 μm, the index of refraction (n₁₀₆_(c) ) for the second reflecting layer 106 c ranges from about 1.3 toabout 2.0. In some embodiments, at a wavelength ranging from about 1.0μm to about 3.0 μm, the index of refraction (n₁₀₆ _(e) ) for the secondreflecting layer 106 e ranges from about 1.3 to about 2.0. In someembodiments, at a wavelength ranging from about 1.0 μm to about 3.0 μm,the index of refraction (n₁₀₆ _(b) ) for the second reflecting layer 106b ranges from about 1.6 to about 2.8. In some embodiments, at awavelength ranging from about 1.0 μm to about 3.0 μm, the index ofrefraction (n₁₀₆ _(a) ) for the second reflecting layer 106 d rangesfrom about 1.6 to about 2.8.

In some embodiments, a reflectivity of the second reflecting region 106ranges from about 80% or greater. In some embodiments, the secondreflecting region 106 reduces light leakage since the second reflectingregion 106 is a high reflectivity structure. In some embodiments, thenumber of second reflecting layers ranges from about 2 layers to about20 layers. In some embodiments, the thickness of each second reflectinglayer 106 a, 106 b, 106 c, 106 d and 106 e ranges from about 60 nm toabout 500 nm. In some embodiments, the second reflecting region 106 isformed by CVD, ALD, or other processes. In some embodiments, the secondreflecting region 106 has a multilayer structure and is formed in amultiple-step process.

First conductive line 116 extends through second reflecting region 106and partially through semiconductor region 102 and first insulatingregion 112. First conductive line 116 is used to electrically connectfirst conductive layer 122 to first doped region 108 by first contactregion 108 b. In some embodiments, first conductive line 116 is a metalline, a via, a through silicon via (TSV), an inter-level via (ILV), oranother suitable conductive line. In some embodiments, first conductiveline 116 includes copper, cobalt, aluminum, nickel, titanium, tungstenor another suitable conductive material. In some embodiments, firstconductive line 116 is a same material as first conductive layer 122. Insome embodiments, first conductive line 116 is a different material fromfirst conductive layer 122. In some embodiments, first conductive line116 includes one or more conductive line portions. In some embodiments,first conductive line 116 partially extends through a center region offirst insulating region 112.

First conductive layer 122 is adjacent to second reflecting region 106and is used to electrically connect to the first doped region 108 by thefirst conductive line 116. In some embodiments, first conductive layer122 is below the second reflecting region 106. In some embodiments,first conductive layer 122 is flush against second reflecting region106. In some embodiments, the first conductive layer 122 includes morethan one conductive portion. In some embodiments, first conductive layer122 is in a two-dimensional plane. In some embodiments, first conductivelayer 122 is a three-dimensional structure. In some embodiments, thethree-dimensional structure includes a combination of conductive lineson different layers of BSI photodetector structure 100. In someembodiments, first conductive layer 122 extends parallel to the secondreflecting region 106. In some embodiments, first conductive layer 122extends along an angled direction with respect to an x-axis and a y-axisof BSI photodetector structure 100.

In some embodiments, first conductive layer 122 includes a single portfor either receiving or outputting an electrical current. In someembodiments, first conductive layer 122 includes more than one port andis capable of both receiving and outputting an electrical current. Insome embodiments, first conductive layer 122 includes copper, cobalt,aluminum, nickel, tungsten, titanium, or another suitable conductivematerial. In some embodiments, a thickness of the first conductive layer122 ranges from about 0.5 μm to about 5 μm.

Second conductive line 118 extends through second reflecting region 106and partially through semiconductor region 102 and second insulatingregion 114. Second conductive line 118 is used to electrically connectsecond conductive layer 124 to first doped region 108 by second contactregion 108 c. In some embodiments, second conductive line 118 is a metalline, a via, a through silicon via (TSV), an inter-level via (ILV), oranother suitable conductive line. In some embodiments, second conductiveline 118 includes copper, cobalt, aluminum, nickel, titanium, tungstenor another suitable conductive material. In some embodiments, secondconductive line 118 is a same material as second conductive layer 124.In some embodiments, second conductive line 118 is a different materialfrom second conductive layer 124. In some embodiments, second conductiveline 118 includes one or more conductive line portions. In someembodiments, second conductive line 118 partially extends through acenter region of second insulating region 114.

Second conductive layer 124 is adjacent to second reflecting region 106and is used to electrically connect to the first doped region 108 by thefirst conductive line 116. In some embodiments, second conductive layer124 is below the second reflecting region 106. In some embodiments,second conductive layer 124 is flush against second reflecting region106. In some embodiments, the second conductive layer 124 includes morethan one conductive portion. In some embodiments, second conductivelayer 124 is in a two-dimensional plane. In some embodiments, secondconductive layer 124 is a three-dimensional structure. In someembodiments, the three-dimensional structure includes a combination ofconductive lines on different layers of BSI photodetector structure 100.In some embodiments, second conductive layer 124 extends parallel tosecond reflecting region 106. In some embodiments, second conductivelayer 124 extends along an angled direction with respect to an x-axisand a y-axis of BSI photodetector structure 100.

In some embodiments, second conductive layer 124 includes a single portfor either receiving or outputting an electrical current. In someembodiments, second conductive layer 124 includes more than one port andis capable of both receiving and outputting an electrical current. Insome embodiments, second conductive layer 124 includes copper, cobalt,aluminum, nickel, tungsten, titanium, or another suitable conductivematerial. In some embodiments, a thickness of the second conductivelayer 124 ranges from about 0.5 μm to about 5 μm.

Third conductive line 120 extends through second reflecting region 106and partially through semiconductor region 102. Third conductive line120 is used to electrically connect third conductive layer 126 to seconddoped region 110. In some embodiments, third conductive line 120 is ametal line, a via, a through silicon via (TSV), an inter-level via(ILV), or another suitable conductive line. In some embodiments, thirdconductive line 120 includes copper, cobalt, aluminum, nickel, titanium,tungsten or another suitable conductive material. In some embodiments,third conductive line 120 is a same material as third conductive layer126. In some embodiments, third conductive line 120 is a differentmaterial from third conductive layer 126. In some embodiments, thirdconductive line 120 includes one or more conductive line portions.

Third conductive layer 126 is adjacent to second reflecting region 106and is electrically connected to the second doped region 110 by thethird conductive line 120. In some embodiments, third conductive layer126 is below the second reflecting region 106. In some embodiments,third conductive layer 126 is flush against second reflecting region106. In some embodiments, the third conductive layer 126 includes morethan one conductive portion. In some embodiments, third conductive layer126 is in a two-dimensional plane. In some embodiments, third conductivelayer 126 is a three-dimensional structure. In some embodiments, thethree-dimensional structure includes a combination of conductive lineson different layers of BSI photodetector structure 100. In someembodiments, third conductive layer 126 extends parallel to secondreflecting region 106. In some embodiments, third conductive layer 126extends along an angled direction with respect to an x-axis and a y-axisof BSI photodetector structure 100.

In some embodiments, third conductive layer 126 includes a single portfor either receiving or outputting an electrical current. In someembodiments, third conductive layer 126 includes more than one port andis capable of both receiving and outputting an electrical current. Insome embodiments, third conductive layer 126 includes copper, cobalt,aluminum, nickel, tungsten, titanium, or another suitable conductivematerial. In some embodiments, a thickness of the third conductive layer126 ranges from about 0.5 μm to about 5 μm.

A first conductive layer 122 and third conductive layer 126 are placedadjacent to another and separated by a distance D1. The placement of thefirst conductive layer 122 and third conductive layer 126 forms a firstopening 128 between each conductive layer. The first opening 128 has awidth of distance D1. In some embodiments, the distance D1 is a diameterof the first opening 128. In some embodiments, first opening 128 iscircular, rectangular, square, hexagonal, or other geometric shapes.

A second conductive layer 124 and third conductive layer 126 are placedadjacent to another and separated by a distance D2. The placement of thesecond conductive layer 124 and third conductive layer 126 forms asecond opening 130 between each conductive layer. The second opening 130has a width of distance D2. In some embodiments, the distance D2 is adiameter of the second opening 130. In some embodiments, second opening130 is circular, rectangular, square, hexagonal, or other geometricshapes.

In an embodiment, the BSI photodetector structure 100 receiveselectromagnetic radiation from an electromagnetic radiation source (notshown) on the backside surface, e.g., first side 102 a. In someembodiments, an optical bandwidth, e.g., measured as a full-width athalf maximum (FWHM), of the BSI photodetector structure 100 ranges fromabout 0.5 Gigahertz (GHz) to about 50 GHz. In some embodiments, awavelength of the received electromagnetic radiation ranges from about200 nm to about 2000 nm. In some embodiments, the electromagneticradiation includes ultraviolet light, visible light or infrared light.In some embodiments, the BSI photodetector structure 100 has improvedsensitivity by utilizing a resonant cavity to enhance the opticalintensity inside the absorption region, e.g., semiconductor region 102.

In some embodiments, an intrinsic Quantum Efficiency of the BSIphotodetector structure 100 ranges from about 1% to about 100%. In someembodiments, a Responsivity of the BSI photodetector structure 100ranges from about 0.1 A/W to about 10 A/W.

FIG. 2 is a cross-sectional view of a BSI photodetector structure 200 inaccordance with one or more embodiments. BSI photodetector structure 200is an embodiment of BSI photodetector structure 100 (shown in FIG. 1)with similar elements. As shown in FIG. 2, similar elements have a samereference number as shown in FIG. 1. In comparison with BSIphotodetector structure 100 (shown in FIG. 1), BSI photodetectorstructure 200 includes a recessed portion 202 of semiconductor region102. The semiconductor region 102 comprises a first side 102 a and asecond side 102 b. The second side 102 b is an opposite side of thesemiconductor region 102 from the first side 102 a. The first side 102 aincludes a recess portion 202, a first surface 204 and a second surface206. The recess portion 202 includes a first recess surface 208, asecond recess surface 210 and a third recess surface 212. The recessportion 202 has a width of distance D3. In some embodiments, the recessportion 202 is circular, rectangular, square, hexagonal, or othergeometric shapes. In some embodiments, a distance D3 ranges from about 3μm to about 150 μm.

In some embodiments, the semiconductor region 102 is partitioned by therecess portion 202. In some embodiments, the recess portion 202 forms amodified semiconductor region 214 of semiconductor region 102. In someembodiments, modified semiconductor region 214 is a central region ofsemiconductor region 102. In some embodiments, the semiconductor region102 includes modified semiconductor region 214. Semiconductor region 102has a corresponding thickness and modified semiconductor region 214 hasa corresponding thickness. In various embodiments, semiconductor region102 has a thickness from a first side 102 a to a second side 102 b. Insome embodiments, the thickness of the modified semiconductor region 214ranges from about 0.2 μm to about 5 μm. In some embodiments, thethickness of the semiconductor region 102 ranges from about 0.2 μm toabout 5 μm.

In some embodiments, the first recess surface 208 is below the firstsurface 204 or second surface 206. In some embodiments, the first recesssurface 208 is substantially horizontal. In some embodiments, the secondrecess surface 210 is substantially vertical. In some embodiments, thethird recess surface 212 is substantially vertical. In some embodiments,the first surface 204 is substantially horizontal. In some embodiments,the second surface 206 is substantially horizontal. In some embodiments,the first surface 204 and the second surface 206 are substantiallycoplanar.

In some embodiments, the first reflecting region 104 is flush againstthe first side 102 a of the semiconductor region 102. In someembodiments, the first reflecting region 104 is in a two-dimensionalplane which is parallel to the first surface 204 of the semiconductorregion 102. In some embodiments, the first reflecting region 104 is in atwo-dimensional plane which is parallel to the second surface 206 of thesemiconductor region 102. In some embodiments, the first reflectingregion 104 is in a two-dimensional plane which is parallel to the firstrecess surface 208 of the semiconductor region 102. In some embodiments,the first reflecting region 104 is in a two-dimensional plane which isparallel to the second recess surface 210 of the semiconductor region102. In some embodiments, the first reflecting region 104 is in atwo-dimensional plane which is parallel to the third recess surface 212of the semiconductor region 102.

In some embodiments, the recess portion 202 of BSI photodetectorstructure 200 has improved sensitivity by utilizing a resonant cavity toenhance the optical intensity inside the absorption region, e.g.,semiconductor region 102. In some embodiments, the thickness of eachfirst reflecting layer 104 a, 104 b and 104 c is controlled in order tocollect sufficient radiation.

In some embodiments, an intrinsic Quantum Efficiency of the BSIphotodetector structure 200 ranges from about 1% to about 100%. In someembodiments, a Responsivity of the BSI photodetector structure 200ranges from about 0.1 A/W to about 10 A/W.

In some embodiments, the thickness of each first reflecting layer 104 a,104 b and 104 c is controlled by CMP or wet etch smoothing of the firstside 102 a of semiconductor region 102 after grinding/polishing. In someembodiments, the smoothing of the first side 102 a of semiconductorregion includes silicon wet etching for top surface roughness control.In some embodiments, the recess portion 202 of the semiconductor region102 is formed by grinding the semiconductor region 102 to a thicknessrange of about 100 μm to about 200 μm by CMP. In some embodiments, afterCMP, the recess portion 202 of the semiconductor region 102 is formed bywet etching the semiconductor region 102. In some embodiments, the wetetching includes silicon wet etching. In some embodiments, the siliconwet etching includes using TMAH or KOH; any other suitable material; orcombinations thereof; and a mask including SiNx, SiO₂ or Cu; any othersuitable material; or combinations thereof. In some embodiments, thesemiconductor region 102 is wet etched until the modified semiconductorregion 214 has a thickness range of about 0.2 μm to about 5 μm.

FIG. 3 is a flow chart of a method 300 of making a BSI photodetectorstructure in accordance with one or more embodiments. Method 300 beginswith operation 302 in which at least one first or second doped region,e.g., first doped region 108 or second doped region 110, is formed in asemiconductor, e.g., a semiconductor region 102 (FIG. 1). In someembodiments, at least one first or second doped region is doped withdopants suitable for Silicon, Germanium, SiGe, SiC, GeSn, SiGeSn or GaN.In some embodiments, the first or second doped regions are formed usingimplantation, diffusion or other suitable formation processes. In someembodiments, the first or second doped regions are formed using highenergy implantation or other suitable formation processes.

Method 300 continues with operation 304 in which at least one of a firstor second insulating region, e.g., first insulating region 112 (FIG. 1)or second insulating region 114 (FIG. 1), is formed in the semiconductorregion, e.g., semiconductor region 102 (FIG. 1). In some embodiments,the first or second insulating region is formed using CVD, ALD, spin-onpolymeric dielectric or other suitable formation processes.

Method 300 continues with operation 306 in which a first reflectingregion, e.g., second reflecting region 106 (FIGS. 1 and 2), is formed ona first side of the semiconductor region, e.g., second side 102 b of thesemiconductor region 102 (FIG. 2). In some embodiments, the firstreflecting region comprises a stack of alternating layers of reflectingmaterials, e.g., second reflecting layers 106 a, 106 b, 106 c, 106 d and106 e, with alternating high and low refractive indices. In someembodiments, one or more of first reflecting layers include highrefractive index materials comprising SiNx, AlN, Si, high-k dielectrics;any other suitable material; or combinations thereof. In someembodiments, one or more of first reflecting layers include lowrefractive index materials comprising SiO₂, low-k dielectrics; any othersuitable material; or combinations thereof. In some embodiments, thefirst reflecting region is formed by CVD, ALD, or other processes. Insome embodiments, the first reflecting region has a multilayer structureand is formed in a multiple-step process.

Method 300 continues with operation 308 in which at least a first or asecond conductive line, e.g., first conductive line 116 or secondconductive line 118 (FIG. 1), is formed in the first or secondinsulating region, e.g., first insulating region 112 second insulatingregion 114 (FIG. 2). In some embodiments, the first or second conductiveline is formed using a combination of photolithography and materialremoval processes to form openings in the insulating region. In someembodiments, the photolithography process includes patterning aphotoresist, such as a positive photoresist or a negative photoresist.In some embodiments, the photolithography process includes forming ahard mask, an antireflective structure, or another suitablephotolithography structure. In some embodiments, the material removalprocess includes a plasma etching process, a wet etching process, a dryetching process, an RIE process, laser drilling or another suitableetching process. The openings are then filled with conductive material,e.g., copper, cobalt aluminum, titanium, nickel, tungsten, or othersuitable conductive material. In some embodiments, the openings arefilled using CVD, PVD, sputtering, ALD or other suitable formationprocess.

Method 300 continues with operation 310 in which third conductive line,e.g., third conductive line 120 (FIG. 1), is formed in the firstreflecting region, e.g., second reflecting region 106 (FIG. 1). In someembodiments, the third conductive line is formed using a combination ofphotolithography and material removal processes to form openings in thefirst reflecting region. In some embodiments, the photolithographyprocess includes patterning a photoresist, such as a positivephotoresist or a negative photoresist. In some embodiments, thephotolithography process includes forming a hard mask, an antireflectivestructure, or another suitable photolithography structure. In someembodiments, the material removal process includes a plasma etchingprocess, a wet etching process, a dry etching process, an RIE process,laser drilling or another suitable etching process. The openings arethen filled with conductive material, e.g., copper, cobalt aluminum,titanium, nickel, tungsten, or other suitable conductive material. Insome embodiments, the openings are filled using CVD, PVD, sputtering,ALD or other suitable formation process.

Method 300 continues with operation 312 in which at least one conductivelayer, e.g., first conductive layer 122 (FIG. 1), second conductivelayer 124 (FIG. 1) or third conductive layer 126 (FIG. 3), is formedadjacent to the first reflecting region, e.g. second reflecting region106 (FIG. 1). In some embodiments, the conductive layer is formed usinga combination of photolithography and material removal processes to formopenings in the first reflecting region. In some embodiments, thephotolithography process includes patterning a photoresist, such as apositive photoresist or a negative photoresist. In some embodiments, thephotolithography process includes forming a hard mask, an antireflectivestructure, or another suitable photolithography structure. In someembodiments, the material removal process includes a wet etchingprocess, a dry etching process, an RIE process, laser drilling oranother suitable etching process. The openings are then filled withconductive material, e.g., copper, cobalt, aluminum, titanium, nickel,tungsten, or other suitable conductive material. In some embodiments,the openings are filled using CVD, PVD, sputtering, ALD or othersuitable formation process.

Method 300 continues with operation 314 in which a second side of thesemiconductor region, e.g., first side 102 a of the semiconductor region102 (FIG. 1), is grinded. In some embodiments, the second side ofsemiconductor region is grinded with CMP or other suitable formationprocesses. In some embodiments, the semiconductor region is grinded to athickness range of about 100 μm to about 200 μm. In some embodiments,the semiconductor region is grinded to a thickness range of about 0.2 μmto about 5 μm. In some embodiments, the BSI photodetector structure,e.g. BSI photodetector structure 100 (FIG. 1) or BSI photodetectorstructure 200 (FIG. 2), is connected to a carrier structure, prior togrinding, using a laser bonding process, a conductive adhesive layer, asoldering bump process or another suitable bonding process.

Method 300 continues with operation 316 in which a second side of thesemiconductor region, e.g., first side 102 a of the semiconductor region102 (FIG. 1), is etched. In some embodiments, the second side ofsemiconductor region is wet etched or etched with other suitableformation processes. In some embodiments, the etching of the first side102 a of semiconductor region includes wet etching. In some embodiments,the wet etching includes silicon wet etching. In some embodiments, thesilicon wet etching includes using TMAH or KOH; any other suitablematerial; or combinations thereof; and a mask including SiNx, SiO₂ orCu; any other suitable material; or combinations thereof. In someembodiments, the second side of the semiconductor region is etched untila portion of the semiconductor region, e.g. modified semiconductorregion 214, has a thickness range of about 0.5 μm to about 5 μm. In someembodiments, a recess portion of the semiconductor region, e.g., recessportion 202 of the semiconductor region 102, is formed on the secondside of the semiconductor region, e.g., first side 102 a ofsemiconductor region 102, by etching a portion of the second side of thesemiconductor region, e.g., modified semiconductor region 214, until theportion of the semiconductor region has a thickness range of about 0.5μm to about 5 μm. In some embodiments, the second side of thesemiconductor region is etched for smoothing/roughness control.

Method 300 continues with operation 318 in which a second reflectingregion, e.g., first reflecting region 104 (FIGS. 1 and 2), is formed ona second side of the semiconductor region, e.g., first side 102 a of thesemiconductor region 102 (FIGS. 1 & 2). In some embodiments, the secondreflecting region comprises a stack of alternating layers of reflectingmaterials, e.g., first reflecting layers 104 a, 104 b and 104 c, withalternating high and low refractive indices. In some embodiments, one ormore of the second reflecting layers include high refractive indexmaterials comprising SiNx, AlN, Si, high-k dielectrics; any othersuitable material; or combinations thereof. In some embodiments, one ormore of the second reflecting layers include low refractive indexmaterials comprising SiO₂, low-k dielectrics; any other suitablematerial; or combinations thereof. In some embodiments, the secondreflecting region is formed by CVD, ALD, or other processes. In someembodiments, the second reflecting region has a multilayer structure andis formed in a multiple-step process. In some embodiments, the BSIphotodetector structure, e.g. BSI photodetector structure 100 (FIG. 1)or BSI photodetector structure 200 (FIG. 2), is disconnected from acarrier structure, after the second reflecting region is formed, using alaser debonding process, or another suitable debonding process.

One of ordinary skill in the art would recognize that an order ofoperations in method 300 is adjustable. One of ordinary skill in the artwould further recognize that additional steps are able to be included inmethod 300 without departing from the scope of this description.

One aspect of this description relates to a backside-illuminatedphotodetector structure comprising a first reflecting region, a secondreflecting region and a semiconductor region. The semiconductor regionis between the first reflecting region and the second reflecting region.The semiconductor region comprises a first doped region and a seconddoped region.

Another aspect of this description relates to a backside-illuminatedphotodetector structure comprising a semiconductor region. Thesemiconductor region comprises a first doped region, a second dopedregion, a first side and a second side. The second side is an oppositeside of the semiconductor region from the first side. The first sidecomprises a recess portion. The backside-illuminated photodetectordevice further comprising a first reflecting region on the first side ofthe semiconductor region and a second reflecting region on the secondside of the semiconductor region.

Still another aspect of this description relates to a method of making abackside-illuminated photodetector structure, the method comprisingforming at least one of a first doped region or a second doped region ina semiconductor region, forming a first reflecting region on a firstside of a semiconductor region and forming a second reflecting region ona second side of a semiconductor region.

It will be readily seen by one of ordinary skill in the art that thedisclosed embodiments fulfill one or more of the advantages set forthabove. After reading the foregoing specification, one of ordinary skillwill be able to affect various changes, substitutions of equivalents andvarious other embodiments as broadly disclosed herein. It is thereforeintended that the protection granted hereon be limited only by thedefinition contained in the appended claims and equivalents thereof.

What is claimed is:
 1. A device comprising: a semiconductor regioncomprising: a first doped region extending from a first top surface ofthe semiconductor region to a first intermediate level of thesemiconductor region, wherein the first doped region is of a firstconductivity type, and the first doped region comprises: a contactregion; and a transverse region, wherein the transverse region comprisesa first edge; and a first reflecting region comprising: a first portionover and contacting the first top surface of the semiconductor region,wherein the first portion comprises a second edge flushed with the firstedge of the transverse region; a second portion over and contacting asecond top surface of the semiconductor region, wherein the secondportion is higher than the first portion; and a sidewall portionconnecting the first portion to the second portion.
 2. The device ofclaim 1, wherein the sidewall portion has a lengthwise directionperpendicular to lengthwise directions of the first portion and thesecond portion.
 3. The device of claim 1, wherein the contact regionextends deeper than the transverse region in a direction pointing fromthe first top surface to a bottom surface of the semiconductor region.4. The device of claim 1 further comprising a second reflecting regionunderlying the semiconductor region.
 5. The device of claim 1 furthercomprising: a metal line extending from a bottom surface of thesemiconductor region to the first intermediate level of thesemiconductor region, wherein the metal line is directly underlying thefirst portion of the first reflecting region.
 6. The device of claim 1further comprising: a second doped region extending from a bottomsurface of the semiconductor region to a second intermediate level ofthe semiconductor region, wherein the second doped region is of a secondconductivity type opposite to the first conductivity type; and a thirdregion between and joining the first doped region and the second dopedregion, wherein the first doped region, the second doped region, and thethird region form a P-I-N junction.
 7. The device of claim 1, whereinthe transverse region further comprises a third edge opposite to thefirst edge, and the first portion of the first reflecting region furthercomprises a fourth edge opposite to the second edge, and the third edgeis flushed with the fourth edge.
 8. The device of claim 1, wherein thesecond portion of the first reflecting region is offset from thetransverse region.
 9. A device comprising: a semiconductor regioncomprising: a first doped region comprising: a transverse region; asecond doped region, wherein the first doped region and the second dopedregion are parts of a photodetector; a first surface, wherein the firstsurface comprises surfaces of the first doped region and the seconddoped region, and the first surface comprises first portions, and asecond portion lower than the first portions; and a first reflectingregion overlying and contacting the first portions and the secondportion of the first surface, wherein a portion of the first reflectingregion is recessed lower than the first portions of the first surface toform a recessed portion.
 10. The device of claim 9, wherein an entiretyof the second portion of the first surface is overlapped by the recessedportion of the first reflecting region.
 11. The device of claim 9,wherein the semiconductor region further comprises: a second surface,wherein the first surface and the second surface are opposing surfacesof the semiconductor region, and wherein the device further comprises ametal line extending from the second surface to the first doped region.12. The device of claim 9 further comprising a second reflecting regionunderlying and contacting the semiconductor region, wherein each of thefirst reflecting region and the second reflecting region comprises adistributed Bragg reflector.
 13. The device of claim 12, wherein atleast one of the first reflecting region and the second reflectingregion comprises: a first layer having a first refraction index; and asecond layer having a second refraction index different from the firstrefraction index.
 14. The device of claim 9, wherein a top surface of aportion of the first reflecting region is lower than the first portionsof the first surface.
 15. A device comprising: a photo detectorcomprising: a first doped semiconductor region of a first conductivitytype; a second doped semiconductor region of a second conductivity typeopposite to the first conductivity type; a third doped semiconductorregion between the first dope semiconductor region and the second dopedsemiconductor region, wherein the first doped semiconductor region, thesecond doped semiconductor region, and the third doped semiconductorregion form a photodetector; and a first reflector over and contactingthe first doped semiconductor region, wherein an extending portion ofthe first reflector extends into the third doped semiconductor region,and wherein an entirety of the first doped semiconductor region isoverlapped by the extending portion of the first reflector.
 16. Thedevice of claim 15, wherein the first doped semiconductor region, thesecond doped semiconductor region, and the third doped semiconductorregion form a P-I-N junction.
 17. The device of claim 15, wherein acombined region of the first doped semiconductor region and the thirddoped semiconductor region comprises first top surfaces and a second topsurface between the first top surface, and the second top surface islower than the first top surfaces, and wherein the extending portion ofthe first reflector has a top surface lower than the first top surfaces.18. The device of claim 15, wherein the third doped semiconductor regionhas a dopant concentration lower than a dopant concentration of thefirst doped semiconductor region.
 19. The device of claim 15, whereinthe first doped semiconductor region comprises: a transverse region; anda contact region extending down from a bottom surface of the transverseregion.
 20. The device of claim 15 further comprising a secondreflector, wherein the first reflector and the second reflector contactopposite surfaces of the third doped semiconductor region.